|How do I establish whether or not it's an on board type?|
If the computer has never had a dedicated graphics card installed since it left the factory, you can usually assume that it has an on-board graphics adapter.
To confirm this, open up the case and look where the VGA cable plugs in.
If there isn't a removable card at that location that fits in a slot, the adapter is an on-board type.
Fitting a graphics card is straightforward enough - I fitted one this morning, though I've done it many times in the past. So-called "low end" cards which are just basic non-gaming cards are especially easy to install since they get their power via the slot, with no additional power cables or connectors required.
This tutorial should help you through it: